This claim is largely true. Technically, taking both creatine and protein simultaneously won't give you a unique benefit, but it's important to take both, especially if you are practicing sports or exercising in the gym. These benefits can also be naturally digested simply from food (meat, poultry, fish, etc.). Studies in sports nutrition journals and reviews by credible health sources like Healthline and the Cleveland Clinic consistently find that while combining the two is safe, it doesn’t enhance performance beyond the benefits each already provides. The most important factors for results are consistently taking both protein and creatine and proper training, not necessarily taking creatine and protein simultaneously.
Overall, it is good to take these. Simultaneously, they bring their individual benefits, but there is no additional benefit to taking them together.
Little, Jonathan P et al. “Creatine, arginine alpha-ketoglutarate, amino acids, and medium-chain triglycerides and endurance and performance.” International journal of sport nutrition and exercise metabolism vol. 18,5 (2008): 493-508. doi:10.1123/ijsnem.18.5.493