The American projections about the impact that Brexit would have on the economy tended to be based on figures released by the government of the United Kingdom during the Brexit campaign as well as the Bank of England. As these institutions were campaigning for an In vote, their credibility was compromised and it appears that the result of the Brexit vote was not as catastrophic as pundits supposedly feared.
Yes, the economic growth is overblown. Brexit opponents voiced concern over the long-term economic affects from the "leave" vote and point to emergency actions by the Bank of England in the wake of Brexit as being the catalyst for short-term gains. Additionally, many point to the continuing value decline of the pound and that growth was only in a select few industries, as evidence that these economic gains will be short-lived.
Yes, I do believe that the affects of the Brexit vote were overblown. Many times the media gets out of control when trying to get ratings. The impacts of the Brexit vote were blown out of proportion. This Brexit vote was not done without much consideration into how it impact the lives of those in the U.K. and the economy.
Although the economy has grown after the Brexit vote, the worst is yet to come. The economy is in a decent spot currently because the banks started running damage control the moment the vote was passed. There is still the uncertainty of the future trade deals. Until the free trade deals are locked down, the economy could slump once again.