Liability usually needs negligence to establish it. So was the lot owner negligent? Perhaps. Or perhaps the landscaper was negligent in which case the landscaper might be liable.
The landscaper didn’t bother to ask what the irrigation system was for, or the lot owner didn’t bother to tell them. That sound pretty much like negligence to me.
On the other hand, as you say, the strata insurance might wear it. If not, bill the unit owner and let them chase the landscaper, if they are at fault.