I agree with this. Flowery words from a roleplayed PC do not gain auto-success any more than a player describing in 3rd person what that PC is doing at our table. It's the approach of the PC towards achieving a goal that is important.
But is it really a mistake? In 5e, the DM determines if a roll is appropriate in that there is some uncertainty in the potential outcome of the actions of the PC(s) and there is a meaningful consequence for failure. If the DM didn't call for a roll, then there's simply no roll. Presuming the PC succeeded in their deception without a roll, why would a player ask to make a CHA(Deception) roll if no roll was called for? Only bad things can happen (which might be fun for the table, I'll grant, but likely causes hardship for the PC(s)).
Well, as I said earlier, I don’t recall having ever face this kind of situation where a call was needed but not asked, so it’s only hypothetical. I assume it’s a situation where there should have been a roll so consequences if failed.
But I agree, I’m from the school of thought that a roll should only be asked if the result has real consequences, which doesn’t come up that much in our games. If there is no real consequences, we don’t bother with rolls.
I also think that as a GM, you should not be shy to ask the player what is his real intention. Let’s say a player decide to make a promise to a NPC to try to convince him to join him, I’ll ask the player if he actually mean it, if he intend to keep his promise or if he’s actually lying. If he’s sincere, I’ll make him roll for diplomacy, if not, roll for bluff. When in doubt, you better ask and come up with the player with the best way to deal with the situation.
Also, I hate dump stats, so let’s say a player say something very convincing but his character have low charisma, I’ll make him roll to see if his character was as convincing as him. Same goes for the opposite, if a player have trouble expressing himself but plays a very charismatic character, I’ll make him roll to see if his character found a better way to express himself.