Coolant level low

[Gonda]

Hi all,

I just had my 08 X5 3.0 leaked radiator replaced from an indy shop. Before radiator replacement, I got the message"Coolant level low" once, I kept put in distilled water so there was no more message displayed. But after replaced, I got the "Coolant level low" message displayed again and the tech said the coolant sensor reported wrong information and needed to be replaced as well. He has to order and it would take few days to get there.
My questions are:

Would it be true that the sensor went wrong or the shop did not do a good job?
Is there anything else I should ask the shop to do?

Thanks in advance for your help...