Things happening in 3's happen all the time I think.
I've been in nursing since "77 (1977, not 1877)
working, medical, med-surg, ICU, ED, extended care, and surgery, and believe me, you see things happening in 3"s all the time!!
Really dosen't matter, deaths, code blue, AAA ruptures, etc, they seem to come in 3's.
The trick is, sometimes the 3's are a bit apart, but still close enough to count as a trio, and sometimes they come soooo close together, you can't tell where one set left off, and the next set begins.
Best advice I guess, is when you have a bad thing happen, such as a death like you described, plan on a couple more....soon.