Slowing refers to a change in the derivative, in this context. Slowing growth would be a decrease in change in GDP per year — a decrease in growth. But the claim is that the growth (first derivative) is what’s slowing — that is, the second derivative of GDP w.r.t. time went negative, which does seem to be the case in mid 2018 from the linked chart.
ArtTimeInvestor|16 days ago
Growth in Q1, Q2 and Q3 2018 was higher than anything that came before.
addaon|16 days ago