John sums it up well but to clarify some art questions, I'll add some more info based on my ad background (admittedly I haven't dealt much in print the past 5 years).
While a vector file is best other formats will work fine IF the file is high enough resolution. A large jpg may be fine, but a small jpg will not - enlarging any jpg file will eventually become pixelated, just depends on the file size. Also, keep in mind that just because the proof looks fine on the computer screen does not guarantee it will look fine on the actual banner. A standard computer monitor is only 72 dpi (dots per inch) - professionally printed materials are at least 600 dpi, generally 1200 dpi and sometimes even more depending on the equipment the printer has. I would guess these banners are 1200 dpi.
Regarding my banners, I accept full responsibility. I must not have used the vectored file - I think I tried it and the file size was too large.
