Wrong. That is not the only way. He can't be our president if the person saying "our president" is not American. In this case, the person saying it claimed to be Canadian. It's just like if a Danish person said to me "our president" i would say "not our president" because I am most certainly not Danish.
Oh dear, another reason to pile on Trump. It never ends does it? I don't think it's going to. The attacks are going to just increase as the campaign goes on.
A lot of presidential candidates don't pay for their security bills. Obama didn't, but it wasn't a big deal for him. These cities didn't have a contract requiring payment. The secret service never agreed to pay that I can see. It's just more pile on Trump news.