Proper Use of "Disponibility"

Solution 1:

My guess is that the person who used it is a native French speaker and translated disponibilité with the closest sounding cognate. (Could be similar in Spanish, I don't know.) I say this because disponibilité is extremely common in French where we would use availability (e.g. "pas de disponibilité" for an apartment or job that is taken).

Interestingly, the more common way this Latin root "-pon-" is borrowed is "pose," and indeed we do borrow this French word with "pose," e.g. in the expression "at your disposal" = "available to you." Of course, if he had thanked you a lot for your disposal, that might have been even more confusing...

Solution 2:

I recognised it, as did @hunter, as the French for 'available', but was a bit surprised to find that 'disponible' is actually recognised by the OED as an English word. (Goodness knows how it is pronounced; not the French way, that's for sure)

disponible, adj. (and n.) View as: Outline |Full entryQuotations: Show all |Hide all Pronunciation: ( /dɪˈspəʊnɪb(ə)l/ ; freq. as French /dispɔnibl/ ) Etymology: < Latin dispōnĕre to dispone v. + -ble suffix; Compare French disponible. Thesaurus »

Capable of being disponed or assigned. Also absol. as n.

1965 Punch 24 Mar. 447/3 One's picture of the higher civil servant—adroit, informed, disponible, never in the way or out of it.

Solution 3:

As a native french speaker, I can confirm you that the guy who told you "Thank you for your disponibility" wanted to tell you "Thank you for your availability!". This mistake is often made by french people. As hunter said, "disponibilité (french word)" => "availability".