Diffing_Engine: Fix incorrect method reporting in IDiffing()

[alelom]

Issues addressed by this PR

Closes #2898

Test files

See #2898

Changelog

Additional comments

[IsakNaslundBh]

Code change looks good, and makes sense. As long as the bot comes through ok this can be merged safely.

[IsakNaslundBh]

@BHoMBot check required

[bhombot-ci]

@IsakNaslundBh to confirm, the following actions are now queued:

• check code-compliance
• check documentation-compliance
• check project-compliance
• check core
• check null-handling
• check serialisation
• check versioning
• check installer

[FraserGreenroyd]

@BHoMBot check copyright-compliance
@BHoMBot check dataset-compliance
@BHoMBot check unit-tests
@BHoMBot check ready-to-merge

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

• check copyright-compliance
• check dataset-compliance
• check unit-tests
• check ready-to-merge

There are 9 requests in the queue ahead of you.