Welcome, JCG.
In addition, there are 5 verbs in all. Three are definitely not past participles. I've marked those off in blue; one is definitely a past participle, and it's not a 'verb' per se, it's part of a verb, notably elliptical,
...(which was) held at... The verb,
greeted, as svartnik mentions, looks like a simple past verb as well as a past participle. It could be short for elliptical
(had) greeted, which is a past perfect verb. Past perfect verbs, as you know, connect two events in time. The verb carrying past perfect morphology happens first in the series of events. Do you see two events connected here, and if so, can you establish that
had greeted happened first? If you can, then, yes, you can safely say that
greeted functions as a past participle. If, however, your can't find that connection, then
greeted functions as a simple past verb.
"It
is my pleasure
to welcome you to the city of Toowoomba." This
is how Councillor Lyle Shelton
greeted 137 new international students at their official welcome
held at the Southern Cross University campus.
All the best.