Ah, you are saying that is what Niantic told you.
Another user found that this mural does exist in real life, but it exists 700m away from your submission location. Even a few meters can be a cause for suspension (not often, but people do commit deliberate abuse), so 700m is quite extreme.
A single error like this is unlikely to cause a long suspension.
Regarding the graffiti, it is worth distinguishing being murals (authorised art, often using spray paint, which are trying to improve an area) and graffiti (non-authorised art, often using spray paint, which are tags and random stuff which tend to have a negative impact on an area), as the former are usually eligible and the latter are usually not eligible.
If your submissions and genuine murals, describe them as murals not graffiti to avoid confusion.
See Unique Art (as posted above by @cyndiepooh).