Was your birthday on a work day last year and a weekend this year? Maybe they simply thought it was appropriate to wish you a happy birthday on the day-of last year and this year just to ask afterward if they didn't see you on the day.
I agree that it seems odd not to get you a card or anything, if they got you a nice present last year. Maybe they are just busy and forgot what they did last year. Sorry they didn't mention it, OP!