They're not wrong. Assuming alternating hands are doing the throwing (rather than both hands throwing a ball simultaneously), 4-ball patterns mean each ball is in the air for 4 beats, while 3-ball patterns only take 3 beats each.
And once one realises that many juggling patterns can be understood by the number of beats each ball takes to return to a hand, one can then think in siteswap (https://juggle.fandom.com/wiki/Siteswap).