With no attack, an ARP table might look like:
192.168.0.1 11-11-11-11-11-11
192.168.0.20 22-22-22-22-22-22
192.168.0.30 33-33-33-33-33-33 <--about to attack
When the attack launches, an entry in the ARP table is overwritten with the attacker's MAC.
192.168.0.1 11-11-11-11-11-11
192.168.0.20 33-33-33-33-33-33
192.168.0.30 33-33-33-33-33-33 <--attacking
So, yes, there are multiple IP entries for the one MAC. And yes, the table entry is overwritten. So the 2 articles are saying the same thing. They do not contradict.
ARP is very simple, so the table is updated with the latest broadcast, which is why arpspoofing tools send out broadcasts frequently.