That is my understanding too. Most of the actual weapons were smuggled in through the tunnels via Egypt.
What I have read is that Iran loads a ship. The ship goes to Yemen and then to Somolia. The weapons are then loaded on a truck. Then brought to the Sinai where they are unloaded and brought by hand into Gaza through the tunnels.
The Egyptian’s could stop them IF they really wanted or at least most of them. However, they do not. So, that means someone is getting PAID to look the other way. It is not just some poor Egyptian Army Border guard either. They may get a small cut. The Egyptian generals are getting paid by Iran to let the weapons flow.
Someone significant is, more than one likely. But the Sinai has a not insignificant terror presence, and Egyptian officers have been known to be sympathetic with the Muslim Brotherhood, so it’s not much of a stretch. And pre October, Israel didn’t make much of an effort destroying tunnels anywhere.
Its the Bedouins in the Sinai that give Egypt all the trouble.