Technically, only monsters can have "multiattack", you mean "extra attack". But it is otherwise correct. I personally only allow the PAM extra attack if it is used two handed, but that is a houserule.The term "two-weapon fighting" in 5e refers specifically to a bonus attack. The rules state that both weapons must be light (barring a feat) and the character does not receive damage bonus from the offhand. I believe RAW this only refers to using the bonus action to attack with a second weapon and does not apply to multi-attack.
Say a 5th level fighter has a longsword in one hand and a spear in the other. To my knowledge there is nothing to prevent the fighter or other character with multi-attack making one attack with the long sword and his second attach with the spear.
My understanding is this is totally legal in terms of RAW and both of these attacks in this scenario would get his strength bonus because they are both a normal attack as part of the attack action and this is not "two-weapon fighting".
If the character had polearm master he could follow this up with a bonus action attack with the butt of the spear for 1d4+strength.
Is this a correct interpretation of the rules?