If you use a good brand 5w 30 fully synthetic engine oil ,then you should be looking at minimum 10,000 miles oil changes or 2 years ,which ever comes first!
You can of course ,change your oil when ever you like ,at 6000 miles ,like Bigwave does,but thats just throwing money down the drain!!
Your blown turbo wasnt because of your "late" oil change,unless your previous oil change was with 15 w 40 oil and 30,000 miles or so !!!
I must say that 90,000 miles is a bit early for them to blow ,unless something unusual happened!Get your mechanic to check the oil feed line to the turbo to make sure its not blocked and check the air filter pipe to the turbo to see if it has any "shavings" that could have been sucked up the turbo!This is something that happened to a member here,as there was some debris in this pipe ,which resulted in blowing more than one turbo.In either case ,since you have loads of smoke from your exhaust ,your turbine/compressor will be broken.Usually ,what happens is the turbine ends up stuck in the cat and the compressor will have shed aluminiumj shavings to your air filter pipe due to it spinning freely against the turbo inlet.
Get your mechanic to check the exhaust for debris .
When turbo blows,it will also push a lot of oil to your intercooler and your mechanic will need to clean it all out.This is very important so as to avoid the engine running on its own oil,just like that youtube video you posted.
Good luck.Hope it all works nicely and you get your X5 back on the road ,as good as new