Carole Walker added that Mr Cameron, who wore a fresh shirt as he chatted to voters in Torquay later, was "unruffled" and continued on his way out of the building.
She added that although the egg did strike Mr Cameron's shoulder, it was his protection officer who took the full force of the mess.
The yolk also stained Mr Cameron's white shirt. A 16-year-old student - who was wearing a hooded top - was arrested briefly but then released.
According to a Conservative aide, the young man was quickly released after police established that he was not carrying any more missiles.
A spokeswoman for Cornwall College, which Mr Cameron had been visiting at the time of the incident, said she was "extremely disappointed that the actions of one student marred this otherwise excellent opportunity to engage students in the election process".
The college's student union president, Toni Pearce, said it was not acceptable and it was disappointing the incident had happened.
The remnants of the egg thrown at David Cameron
She said: "But these things happen and it's probably an expression of a lot of anger people have towards politicians at the moment.
"A lot of students and members of the public see them as comedy figures rather than to be taken seriously."
Mr Cameron's response was more restrained than that of former Deputy Prime Minister John Prescott, who punched a protester who threw an egg at him during the 2001 election campaign.
Speaking later in Cardiff, Gordon Brown said he was "sorry if anything had happened". He added: "We want to have a fair campaign. We want people to behave themselves and not doing these things."
Before the incident, Mr Cameron shrugged off opinion polls pointing to a hung Parliament, telling students "polls go up, polls go down".
"I've been leader of this party for four and a half years, I've been 10 points ahead, I've been 10 points behind," he added. "What I'm interested in is the big poll on 6 May."
In a speech later in Torquay, Mr Cameron set out a seven-point plan to make politicians and ministers more accountable, claiming the old political system needed to be "blown apart".
Among the pledges are a curb on quangos, which Mr Cameron said had become "a law until themselves", more "open primaries" to choose Conservative candidates and a referendum before any further powers are transferred to Brussels.
"Those are all simple steps, all steps that would make a difference, all steps that people I think will understand would go to the heart of what is wrong with our politics," he said.
"That's what needs to change in our system, that's the simple, straightforward, believable, doable change you will get from the Conservative government."
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