Often enough, the use of flaps is concurrent with the extension of landing gear. The gear will assuredly cause a pitch down.

Again these are flapperons, NOT FLAPS. Unlike flaps (particularly in landing configuration), flapperons are most often full span & only deployed at a shallow angle -- this causes an immediate increase in angle of incidence, & results in pitch-up, regardless of wing configuration. The pitch-up is speed sensitive. The pilot can manually compensate for the pitch-up, or as in this case, he can mix in some down elevator. The down-mix is also speed sensitive -- it is also not in-flight adjustable.

Rcrmel has mixed in too much down trim.