This can happen sometimes. The repeater may have multiple input tones for various users, and someone else just unluckily had the same freq/tone combo to open the repeater. may even have been a ducting phenomenon. A lot of folks whine and moan and groan about digital, but you won't see this on an digital platform. Anyway, these issues are fixed usually very quickly. (Here's to hoping they do not have the input tone set to CSQ as that would just be stupid and asking for interference from anyone!)