I ran the stats for Orr's 1970-71 season from the Hockey Summary Project, and also the numbers for some other players to compare.
I see that nik jr already posted reckoning's research on this, but I'll add what I have.
Here are Orr's numbers broken down vs the rest of the original six teams and vs the expansion teams.
Orr vs O6: 30 GP, 11 G, 35 A, 46 P, 1.53 Pts/G
Orr vs Exp: 48 GP, 26 G, 67 A, 93 P, 1.94 Pts/G (26% higher than vs O6)
I also ran the numbers for a few other top players from that season to compare. I selected players who played a full 78 game season so I didn't need to find out who missed which games.
Phil Esposito vs O6: 30 GP, 30 G, 31 A, 61 Pts, 2.03 Pts/G
Phil Esposito vs Exp: 48 GP, 47 G, 39 A, 86 Pts, 1.79 Pts/G (12% lower than vs O6!)
Bobby Hull vs O6: 30 GP, 12 G, 14 A, 26 Pts, 0.87 Pts/G
Bobby Hull vs O6: 48 GP, 32 G, 34 A, 66 Pts, 1.48 Pts/G (59% higher than vs O6)
Jean Ratelle vs O6: 30 GP, 6 G, 16 A, 22 Pts, 0.73 Pts/G
Jean Ratelle vs Exp: 48 GP, 18 G, 29 A, 47 Pts, 0.98 Pts/G (34% higher than vs O6)
Tom Webster vs O6: 30 GP, 6 G, 9 A, 15 Pts, 0.50 Pts/G
Tom Webster vs O6: 48 GP, 24 G, 28 A, 52 Pts, 1.08 Pts/G (119% higher than vs O6)
In 1970-71 the group of Esposito, Hull, Ratelle, and Webster scored 27% more against expansion teams than against the rest of the original six teams. Orr scored 26% more against expansion teams. His increase in scoring was basically average for a star player of the time. At least for this season, he didn't fatten his scoring totals against weak teams more than other top scorers.
Note: Some of the Hockey Summary Project's numbers are slightly off the official numbers for this season. For example, they have Esposito with 77 G and 70 A, which is probably the biggest difference.