It makes sense just fine. The research about latency tolerance informed the design constraints for packet-switched digital phone networks, which had been proposed since the 1950s and began to replace POTS in practice in the 1980s (e.g. System X in London in 1980).
Latency requirements constrain routing and buffering specs. Packet switched voice could not work until the system could meet human tolerance of latency.
While that is true, at a certain point, more latency in a working system costs money, especially at the earlier switched systems
But yeah, they needed to do a research about it, but I would doubt "The first research project Bell labs did", since Bell Labs predates digital phone networks
Sure, but no-one is ever talking about deliberately over-long latency. There's a sweet spot where packet-switched is fast enough, while cheap because of shared bandwidth and routing flexibility. It costs more to go faster, but it's game over to go slower than humans will accept.
And it's unlikely that the poster was referring to direct (non-packet) connections since these have been rare for a long time.
Latency requirements constrain routing and buffering specs. Packet switched voice could not work until the system could meet human tolerance of latency.