To answer your question, Pokemon transferred over from different games can be disobedient, as they have different OT's than the trainer you're playing as in BDSP. Assuming that you only have the first badge in the game, Pokemon over level 10 and with a different OT will disobey you until you get the second badge, which will allow any Pokemon below level 30 to follow your commands. So, if you only have the first badge, that's likely why your Pichu disobeyed you.
Don't worry too much about disobedience though! It shouldn't be much of a hassle later in the game, and it shouldn't hinder your gameplay at all by the time you get the 4th gym badge.
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