I am not an expert on interpreting these results, so others may have more to add. That said, some comments:

• I agree that wear metals are high. If the sample was taken cleanly, and the lab results are correct, then you should be watching the trend lines on the wear metals over the next few oil changes.
• I don't see why iron relates to piston scuffing, but maybe someone can enlighten me. Maybe they think you have iron cylinder liners (you don't). It seems like a computer generated comment to me. If you did have a problem with piston scuffing, I would expect that you would have noticed high oil consumption.
• Remember that this report is measuring elements in parts per million. One part per million represents 0.0001%. If you had material breaking up in the engine you would need to do some type of large particle analysis to determine the source, not rely on a spectroscopic analysis as was done here. I think this type of analysis shows particles up to about five microns, so if you want to determine the source of any significant wear particles then you need to have a lab do an analysis of the ferrous material, or do a large particle analysis under a microscope. Both are optional tests, but Blackstone doesn't list the ferrous material analysis, just a single particle count option, at additional cost.
• Viscosity measurements show high. That is better than them being low, but they are still out of range, by 10% or so. 15% is often the point at which flags go up. Since you don't know what oil was in the engine, you can't draw any conclusions from these measurements, other than noting they are high. Perhaps a previous owner used an oil treatment product.
• The insolubles are good, indicating that there are not abrasive materials in the oil. That tells us that the oil has not oxidized, and that the oil filter is doing a good job. Thought you would like some good news.
• You didn't buy the TBN test (total base number). That would have indicated how the additives in the oil are doing, whether they are depleted or not. It speaks to oil life.
• You didn't buy the TAN test (total acid number). That would indicate how many acids had built up in the oil, due to oil degradation. Relates back to oxidation of the oil.
• I think Blackstone's suggestion to watch your coolant level is good. You should also be tracking oil consumption.
• The universal averages they show are based on 10,000 km oil life. Since you don't know how long the oil has been in there, the averages they list don't mean very much. I wouldn't be too harsh on them for this, since they have nothing to go on, not knowing the oil life, the amount of make up oil added, etc. I would question some of the conclusions they have come up with from a single analysis; these are possible contributors, not a diagnosis. If I was your BMW dealer, I would rightly dismiss your claim based on that fact.

Comparing the figures to your Subaru doesn't mean anything. You want to compare these figures to your next few oil samples. You also need to establish a baseline in terms of knowing what oil (type, viscosity) is in the engine.

The owner's first service likely included an oil and filter change, since it was free (along with the micro-filter). You want the service history, to see all the dealer-performed services. That history won't show non-dealer performed services of course.

The SOS labs (Scheduled Oil Sampling) are a trademark of another organization than Blackstone, namely Caterpillar dealers, operating independently around the world, to a set of Caterpillar standards.

I see nothing from what you have reported that suggests your engine is failing and that the dealer you bought it from should do anything about it. A physical inspection of the engine may reveal that something is failing, it is just that these results are not sufficient to conclude that.

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