What does Dirgha AyushmAn bhavah mean?

When Periyavaa was giving darshan, four or five Vidwans who had come for darshan, were sitting on the floor.
In the course of his conversation (with the devotees), Periyavaa asked them, "When Bhaktas do namaskaram to me, I bless them with the name ‘Narayana, Narayana’. What do you people who are samsAris say for blessing?”
"We say, ‘[b]dIrgha AyushmAn bhavaH[b]‘; only that is the custom.”
"What does it mean?”
"Remain in saukyam for a long time’ is its meaning.”
Periyavaa asked all the Vidwans present there, one by one. Everyone said the same meaning.
Periyavaa remained in silence for sometime. Then he said, "The meaning you all said is a wrong one.”
The Pandits were taken aback. Everyone of them was a bade bade Vidwan, and had earned the Siromani title.
For the Samskrta Vaakyam ‘Dirgha AyushmAn bhavah’ even those with a little knowledge of Samskrtam can tell the meaning. Such simple words! Yet Periyavaa says the meaning is wrong?
"Shall I tell it myself…..?” The Pandits sharpened their ears.
"Of the twenty-seven Yogas, one is named AyushmAn. Of the eleven KaraNas, one is the called the Bhava. Among the week days, the Saumya Vaasaram falls on a Wednesday. When all these three–on a Wednesday, the AyushmAn Yoga and the Bhava KaraNa–occur together, that day is said to be shlAgya. Therefore, if these three occur together, whatever good phalas would be got, I bless that you may get all those fruits…”
All the Vidwans got up in together and did namaskaram to PeriyavaaL.