From page 24 of the (English) rulebook.
Brood Lord Cards
Brood Lord cards are treated exactly like
Genestealer cards with the following exceptions:
• Brood Lord cards are never shuffled into the
Genestealer deck or into a blip pile. They only
spawn when specified by a Location card,
and spawn without being in blip piles.
• Brood Lords have two movement icons,
and their swarm will move when either
icon is activated.
• A Brood Lord may not be slain if it would leave
a normal Genestealer card in the swarm. In other
words, the Brood Lord must be the last Genestealer
in the swarm to be slain.
• When a swarm containing a Brood
Lord attacks, subtract 1 from its die roll.
Therefore, the swarm is more likely to
slay the defending Space Marine.
Intimidation works on them.
Sorry, went and read the actual ability of Intimidation.
Shuffling them into a blip pile goes against the first exception.
You are correct in your play.