Increased deliveries of commercial and military jets buoyed Boeing's results, and sales topped forecasts. Its stock gained more than 7%.
Specifically, he thinks the company needs to make its iPhones more useful by adding technology like sensors for health care and fitness.
"If the key drivers are around app stores and the other services business, they will slow, "he said. "I just don't know if investors are quite aware that that is to come relatively quickly."
" We've had these horrific headlines for quite some time, and yet the user base hasn't really left, "he said. "In our view, as long as the folks are there using it, then advertisers need to follow and need to be there"
There could be more news in front of the markets: Wednesday on whether it will raise interest rates. Chairman Jerome Powell will deliver remarks following the Board of Governors meeting
Wharton Finance Professor Jeremy Siegel said he's confident The Fed will not hike again. But everyone will be looking at the wording of the Fed's statement.
"In the past year, they've always said there's going to be some gradual rate increases in the future," he said. "Now the market expects them to shift – not put in and say 'we are now pausing in our rate increases and assessment our increases and how they will affect the economy in 2019." "
If the Fed's statement doesn" t reflect such a shift, Siegel said, he expects to be "a lot of disappointment" in the markets.
Siegel added that he is not concerned about the overall US economy. He sees "no signs that it's entering a permanent slowdown or even a recession."
On Wall Street, Siegel isn't concerned about Brexit or another US government shutdown. More troubling, he said, would be an escalation of the US-China trade war.
CNN Business staff contributed to this report.