Find My Friends app accuracy
The exact location shown by the Find My Friends (or the Find My iPhone) service can be off somewhat, and the distances can be a lot more than what you've described.

For example, in our household we have about 20 devices. We also live on acreage and back onto an environment reserve. Sometimes, when using the Find My iPhone service, I can see one or more devices appear as if they're in our next door neighbour's yard, somewhere within the bush surrounds of the reserve, in the creek, and so on.

So, while it's impossible for anyone here to give you any certainty on where your boyfriend's device was at the time, we can say that the location being reported could easily be off by a distance of more than just appearing to be across the street. It's also common for it to appear to hop or jump around a little while obtaining the location.