I think that's a substantially overstated (it's Wikipedia after all) account of Caledonian. There had of course been charters long before Caledonian was founded (someone actually did charters to New York with a Handley Page Hermes in the 1950s), and while they were the first with a new type of certificate, there had been other certificate types previously. US carriers had also predominated, and it wouldn't have been the least acceptable for them to operate while their government denied reciprocal rights. British Eagle was a comparable carrier with Britannias, and when secondhand 707s came onto the market there was a great expansion of operators, including Laker in its earliest days who took the Eagle 707s when the latter went under.
The principal Transatlantic work for the US carriers was military charters, mainly to Germany, using DC-6s and Constellations, which gave them a whole lot of unbalanced trips where they looked to the commercial world for backload trips, very often ferrying over from Frankfurt etc to Gatwick for the return flight. The military contracts started stipulating jets from the mid 1960s, and the DC8 was the US carriers principal choice, especially the stretched -61/63s when these came along. There was often a whole gaggle of them from different operators at Gatwick in summer mornings headed for a range of US points. A number of their operators were somewhat high handed, if extra military work came along, as often happened, they would shift flights by a day forward or backwards at short notice, excusing this with "well it's a charter". No EU compensation in those days.