Usual silly opinions. The engines could not have ingested anything from their own exhaust jets. Physically impossible with take-off thrust.
And I witnessed the same thing at MAN, holding to take-off on 23L. A 321 threw some large chunks of concrete rearwards, we reported it, the runway was hastily inspected and then (obviously) closed. We eventually were cleared to taxi gently around the damaged area, and took our place at the back of the big queue for 23R. Having burned a fair amount of fuel...anyway...this can happen anywhere but is particularly likely at crap airports.