Gosh Will... looks like you better put an add in the paper quick looking for lemon tree dating service!!!
Just kidding... I have two Mayer Lemon trees in pots that I bring in every winter and I have had that happen to me before and before long I start to see buds popping up all over. That first flower may just be the start.
However you mentioned that this is the first time it's bloomed. Have you tried fertilizer specialized for promoting blooms?
Deb