I don't know the specific circumstances here but throwing old mom under the bus might be a bit much. I'm a father of two. My 6 year old boy never required much in the way of extra discipline. We never put on cabinet locks or door knob covers because you could just tell him not to do something and he generally wouldn't. A couple years ago we were in a toy store and he asked me for a lego set. When I told him no he said, "That's ok. I'm sure they'll still be there later". Wait, what? And everyone told me I was such a good dad but no, he was who he was despite me, not because of me.
He was just chill. He still is. Then came my daughter. My 3 year old girl is so incredibly sweet but she is the spawn of Lucifer. She straight up does not listen. You look at her and tell her not to do something and she'll look you straight in the eyes and continue to do it. She doesn't touch her toys but straight up destroys anything that looks like she shouldn't be touching it. She screams, she throws toys, she bites, scratches, pulls out her hair... you name it. Sometimes when she gets mad she slowly scans the area around her, looking for possible projectiles before finding something, picking it up slowly and then throwing it. That's some fucked up shit. You're not even acting out of uncontrollable 3 year old rage at that point. That's calm and calculated.
Is it because of poor parenting? No. She's 3. She's been this way since I can remember. Is my 6 year old awesome because of parenting? No, probably not. He just has a different disposition. I am really hesitant to blame bad parenting for the actions of a toddler unless the toddler is actively being poorly parented in the moment. As they get older you can start assigning more responsibility to the parents but for a three year old, I guess without knowing all the details I just can't make that statement with the confidence that some here can.
Now if he's 10 and this is still an issue then sure, blame the parents but 3? Nah, I'm hesitant to blame parents for too much just as I'm hesitant to give them too much credit for anything good.