I get that you'd be upset at the accusation, and obviously on a forum we can't tell tone of voice etc. However I have an office in a rehearsal rooms and unfortunately bands do 'wander off' with equipment on a very regular basis (miss are a particular favourite), I can think of one occasion on which a set of decent Mapex drum stands had mysteriously turned into cheap Stagg ones. When the studio can they do try to be vigilant and often it involves going through diaries and working out who was in when.
You can rest assured that the studio hate making the call just as much as you hate receiving it.
Last week we had a situation where a band took home an expensive CDJ deck. They were called and they'd said it was an accident - I'm not sure how it could've been but still it's been returned and is all water under the bridge.
It's sad that these things happen, and in the majority of cases it's the minority causing the aggro.
I'm glad it all worked out ok for you in the end, if it were me I'd give them the benefit of the doubt, then if anything similar happens again start thinking of using somewhere else.