Matt,
Not sure about OR, but in CA two straps are generally required with specific anchoring. And, as code is rather vague on this, it would be necessary to refer to the installation instructions for the strap kit. In your specific case, there would be no manufacturer's installation instructions as it consists of plumbers' tape. However, In CA the DSA (Division of the State Architect) has drafted recommendations as to how to brace a water heater. 12 pages, in fact. The diagrams clearly show straps anchored to two studs.
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It may be that in OR, you have something similar to the DSA and you might be able to download specific recommendations.