"Bukkake" has a general and perfectly ordinary as well as a more specialised and pornographic meaning. It is merely the noun of the verb "bukkakeru" which means "to throw or splash or slosh [water] over or on [somebody or something]". I.e., one can throw (bukkakeru) water over a fire: hi ni mizu wo bukkaketa (I threw water over the fire). It does, though - and hence the pornographic extension of meaning - also carry especially the connotation of splashing water or other liquid on the face to arouse someone; i.e., wake someone up or alert them or bring them to themselves (i.e., to consciousnes); e.g., Kare no kao ni mizu wo bukkakete, shouki wo tsuketa (I dashed water on his face and that brought him round).
"Bukkake Udon" is a specfic type of cold udon noodle dish, usually accompanied with a thick dashi broth. I suspect it was this dish the "senior citizens" were after!