Is spiked with bitter truth?

Does "is spiked with" mean "is mingled with"?

Context:

Though the details differ across the world, no known culture
lacks some version of the time-consuming, wealth-consuming,
hostility-provoking rituals, the anti-factual, counter-productive
fantasies of religion. Some educated individuals may have
abandoned religion, but all were brought up in a religious culture
from which they usually had to make a conscious decision to
depart. The old Northern Ireland joke, 'Yes, but are you a
Protestant atheist or a Catholic atheist?', is spiked with bitter truth.
Religious behaviour can be called a human universal in the same
way as heterosexual behaviour can. Both generalizations allow
individual exceptions, but all those exceptions understand only too
well the rule from which they have departed. Universal features of
a species demand a Darwinian explanation.