No problem. They pruned it rather than deadheading it. It will be bushier and since it was still spring, it will form many flower buds for next year.

Actually, when deadheading, I don't cut anything. I grab the spongy material at the base of the truss and bend it sideways, breaking it in the middle. It breaks very easily.

Actually, I seldom deadhead. If a plant blooms alternate years or if it gets petal blight, then deadheading is critical. If the plant produces lots of nice healthy flowers, deadheading is mainly cosmetic.

Here is a link that might be useful: How to grow rhododendrons and azaleas.